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Hifiman Jade II


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So, the HFM "rebuttal" does have some interesting points.  

 

1)  1k resistor outputs vs 5.1k for the Stax - no reason given for the change, presumably the cost for either resistor is the same

2)  2M resistor bias outputs vs 5M for Stax - again, no reason given, should be identical cost

3)  op amp input vs discrete MOSFET input. Presumably for cost reasons.

4) output MOSFETS supposedly to increase voltage output capability, claimed very low capacitance, but part number not identified. Are we talking a cascode transistor (bottom) MOSFET (top) combo? Don't know.

5) the text says they are comparing two schematics, however they post the SRA-12S schematic but use photos of the circuit board instead of an actual schematic.

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When I heard these were being released I just had to get a set to see if they matched the supreme crap that the original was.  Now after some delays I picked the set up from the postoffice. 

The srm-001 is an opamp driving a fet that drives a transistor (cascode) into a load resistor and is cap coupled to the output. (cascode differential) The jade2 is an opamp driving a transistor t

I also don't think Fang really understands what is going to happen now.  I'm going to track down a Shangri-la jr. amp no matter the cost just to rip it apart. 

Posted Images

That stuff is just too funny.  So let's start at the beginning, 1k in series with the output is better than nothing (Cavalli, Woo, Kingsound etc.) but it should be around 5K.  How 1K is similar to 5K and offer the same protection is beyond me.  Does anybody at Hifiman understand Ohm's law? 

There are indeed two 2M resistors on that board.  When I initially wrote that I had only looked at the amp board and was still trying to untangle the mess of this build.  Still that should be 4.7M but 4M is close enough. 

Also, while the amp is very reminiscent of the SRA-10S... it does have the opamp input.  You know what amp is based off the SRA-10S and has an opamp inputstage?  The SRM-001... aka the 1995 portable amp.  Yup there are some similarities there as well. 

So the output stage uses FQPF4N90C's as can be seen here:

DSC00028-2-2.thumb.jpg.f750d99e8a01ec3f9567d6054a5c7cfa.jpg

...and the datasheet is here:

http://www.mouser.com/ds/2/149/FQPF4N90C-195517.pdf

Go down into Dynamic characteristics and there we have output capacitance, typical 65pf.  So the headphones are roughly 130pf or so and you have two of these per driver.  Yup, stellar job of keeping the Cob low.  For reference, the 2SC4686A used in the KGSS and KGSSHV, 2.2pf.  So the output capacitance here is just about 30 times higher.  Same goes for what Stax have used for years.  Also, notice the black cans on the source pins, those are inductors for some reason.  Inductance and capacitive loads don't really mix, just look at the train wreck that is the Woo WES. 

For any laymen reading this, many know about the 10 times rule when matching sources to amps.  The goal there is for the input impedance of the amp to be at least 10 times higher than the output impedance of the source.  Same goes for preamps into poweramps etc.  Same thing applies here, how do you think the amp likes driving the capacitance of the headphones when it first has to overcome its own output Cob?  

Bottom line, if anybody like JimL wants to take a look at the Jade2 amp, I'll send it to you for free.  The only things I did to it was simplify the input wiring, as it makes no sense to go from the sockets to the amp PCB, then to the volume control, then back again.  I also redid the earthing of the amp as it was very lacking for CE safety requirements. 

One more thing that amuses me endlessly with Hifiman is that familiar Chinese trait... victim hood.  I still remember it well at Canjam 2010 when somebody gave Tyll a set of HE-5's (I think) to measure and Fang freaked out.  It was his own personal set so he could do what ever he wanted with it but Fang did not approve.  That speaks volumes about his character.  I'm all for right being right but what about addressing the flat out lies in the specs, that a few parts were not properly soldered to the boards or that I'm sure the same crap applies to the 50K$ Shangri-La.  They certainly use the same cable...  ;)

 

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6 minutes ago, spritzer said:

It's on Head-fi so I don't care

It is just a link to a tutorial on caps : https://www.electronics-tutorials.ws/capacitor/cap_7.html (so you can better edumacate yourself, of course...), and the following Pf calculation:

MOSFET C1=65 Pf 
Transistor C2=6 Pf
Ctotal=C1*C2/(C1+C2)
Ctotal=5.49 Pf

Edited by GeorgeP
typo
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It's interesting to see how Hifiman cares about the safety of its customers ... hopefully they will worry about the same way of not releasing versions of their headphones every year.

When will the Jade III be ready? 

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Interesting in Fang’s letter that he touts FCC testing as one reason his shit couldn’t possibly be dangerous. IIRC, FCC testing is for Part 15, which only covers RF emissions (and isn’t applicable to this?). Total BS.


Sent from my iPhone using Tapatalk

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3 hours ago, jose said:

It's interesting to see how Hifiman cares about the safety of its customers ... hopefully they will worry about the same way of not releasing versions of their headphones every year.

When will the Jade III be ready? 

Give them two weeks.  And yeah, it will be more expensive and equally dangerous.

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I also don't think Fang really understands what is going to happen now.  I'm going to track down a Shangri-la jr. amp no matter the cost just to rip it apart.  :rofl:

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I presume this is kosher; not a personal email. Not even sure why I got this... I bought a pair of Massdrop HE4XXs... oh wait, I think I did buy a pair of IEMs direct (and returned them)...

 

image.thumb.png.0ff45d6eb25d5d9cd773b1d20104a65c.png

Edited by Pars
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This is high class stuff from Fang. He should let his PR department handle this shit storm considering he cannot keep his cool. I feel like we are going to see another Fang public meltdown at this rate. He wouldn't always need to be on the defense if he and his company atleast made an honest attempt to take criticism and improve on it from there. The only thing they figured out was how to not make their headbands break. And they could only do this by yeeting ergonomics to the devil.

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On 3/27/2019 at 11:31 AM, spritzer said:

Bottom line, if anybody like JimL wants to take a look at the Jade2 amp, I'll send it to you for free.  

Appreciate the offer but I'm going to be away from home for a month or so visiting friends so, I'm out.

Edited by JimL
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7 hours ago, Pars said:

Well, I feel the ban stick coming. Posted on HF regarding the FCC Part 15 not being applicable. Also called jamato8 out as a known shill from years ago...

Is tomato8 coming out of the woodwork?  Clearly some shilling is needing to be done!  :rofl: 

3 hours ago, JimL said:

Appreciate the offer but I'm going to be away from home for a month or so visiting friends so, I'm out.

Not a problem.  I'll ask Kevin if he wants to rip this one apart...  :)

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The circuit is more like the srm-001 blown up by a bunch. So opamps input, solid state version of grounded grid output stage, resistor loaded, and capacitor coupled output. Positively ancient design by any standard. Did not even replace the power resistors with current sources. Saying that the output capacitance is that low because the two devices are in series clearly shows no understanding on how that design works. And the series output inductors are not a great idea either.

The headphones may be decent, I don't know because I have not heard them, but there are so many decent headphone amps out there that buying the hifiman version seems like a waste of money.

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